1. Field of the Invention
The present invention relates to a display control apparatus for displaying an image on a touch-operable display unit, and a control method thereof.
2. Description of the Related Art
In recent years, a device capable of displaying a plurality of images on a display apparatus that includes a touch panel, and capable of switching the displayed image by performing scrolling according to a touch operation on the touch panel has become widely used.
Japanese Patent Application Laid-Open No. 2011-164129 discusses a technique in which scrolling in an upward direction can be instructed by an upward stroking operation on the touch panel, and scrolling in a downward direction can be instructed by a downward stroking operation on the touch panel, while a plurality of images is being displayed. Further, the images arranged upstream, instead of the images arranged downstream, with respect to a direction in which the images move by scrolling, are displayed first. A large number of images can thus be displayed while scrolling is performed even if the images cannot be displayed sufficiently in time with high-speed scrolling. Furthermore, a greater number of images than the number of images included in a display range are buffered.
If a plurality of displayable images are cached so that scrolling can be performed within the range of the cached images as discussed in Japanese Patent Application Laid-Open No. 2011-164129, scrolling can be performed with high responsiveness. In such a case, if the images that are not cached are to be displayed, the cache is updated according to a cache update instruction, and scrolling can thus be performed within the range of the newly cached images. However, if the operation for instructing scrolling to be performed within the cached images is totally different from the operation for instructing cache updating to be performed for displaying the images that are not cached, operability becomes low. The desired image thus cannot be displayed only by intuitive stroking on the touch panel. On the other hand, if the cache update instruction operation is performed as often as scrolling within the cached images, the cache becomes frequently updated. As a result, the responsiveness with respect to the operation becomes low, and the cache is unnecessarily updated so that processing load is increased.